1. Field of the Invention
This invention relates to manufacture of capacitors. More particularly, it relates to an improved method for forming capacitor elements for incorporation in a capacitor housing by pressing the capacitor element into a form.
2. State of the Prior Art
It is known in the prior art to fabricate wound film capacitors from strips or webs of dielectric material having electrically conductive material formed thereon and formed with a tight coil. Characteristically two or more such webs are wound together with dielectric material between the electrically conductive layers so that the electrodes thus formed are insulated from each other. Various types of materials, forms of encapsulations, and means for coupling terminals to the electrodes have been utilized.
Another capacitor structure and method of their manufacture involves the so-called chip capacitors. These are described in detail by Lavene in U.S. Pat. No. 4,378,620, which is herein incorporated by reference. In summary he describes fabricating small capacitors from a mated pair of dielectric webs having a plurality of electrically conductive spaced-apart electrodes formed thereon. The webs are aligned such that an electrode on one layer is juxtaposed a non-conductive portion of the web on the other layer in a manner such that the electrodes are off-set on the layers and to not lie one above the other. The webs are then wound, and the electrodes and dielectric material are bonded by applying pressure to the coil. Individual capacitors are then formed by chopping the coil into lengths. The layers of conductive material are electrically interconnected at each end, as by metal plating, and terminals are attached thereto. The assembly can be encapsulated or placed in a suitable housing to form the completed capacitor.
Due to the methods used to flatten and bond the coils in the prior art, the capacitors did not have precise forms, and required housings to be of a sufficiently large size to accommodate the capacitor elements. This was true for both discrete wound capacitors and chip capacitors. The additional size of the housing is undesirable for components to be used on printed circuit boards. Further, the irregular shapes create problems in automated assembly systems, and cause problems for environmental sealing.
It has been recognized that capacitors that are encapsulated and permit planar mounting to supporting assemblies are desirable. Such a device was described in co-pending Application Ser. No. 586,014 filed Mar. 5, 1984 and now Pat. No. 4,538,205. There is described a housing of a length somewhat longer than the capacitor element, forming a cavity at each end when the capacitor element is inserted. Conductive material is placed in the cavities for contacting respective electrodes, and end caps are fitted over each end. The end caps make electrical contact and are shaped for permitting surface mounting. An irregular shape of the capacitor element can cause problems of automated handling for insertion in the housing.
An object of the invention is to form capacitors by pressing capacitor elements constructed of interleaved layers of electrically conductive material and dielectric material into a form selected to match the interior shape of an associated housing. The capacitor component is less expensive to fabricate, and has an improved volumetric efficiency.